Derek Watts, a close friend of Charlene's father Mike Wittstock, appeared to unintentionally break the news when he tweeted that Mike had called to tell him he was expecting not one, but two, grandchildren.
"My old Bulawayo schoolmate Mike Wittstock has phoned to say his daughter is pregnant with twins," wrote the South African TV presenter. "Congrats Princess Charlene and Albert!"
Derek deleted his message shortly after posting it, suggesting he had been told that the news was not yet public knowledge.
South African newspaper , the Benoni City Times, reported that excited granddad-to-be Mike also told them he was expecting two more grandchildren.
"I am very happy about the news and now my wife and I are going to have four grandchildren," he told the newspaper, making reference to his sons Gareth and Sean's children.
Monaco officials have confirmed that Charlene, 36, is due to give birth in December, however Charlene and Prince Albert, 56, have neither confirmed nor denied the persistent rumours that she is carrying twins.
This is Charlene's first pregnancy, but Prince Albert is already the father of two illegitimate children - 22-year-old daughter Jazmin Grace Grimaldi, and 10-year-old son Alexandre Coste.
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